In performing a down-shift based on a driver's intention of deceleration, an engine output increasing control is started at a time when a transfer torque capacity of the releasing clutch becomes small or zero and the actual oil pressure decreases to an initial oil pressure, not causing an acceleration feeling even upon the engine output increase. For estimating a time when which the real pressure of the releasing clutch decreases to a level of not higher than the initial pressure, the response of the real pressure relative to an oil pressure command value for the releasing clutch is approximated using a transfer characteristic of "first order lag+time delay." An estimated real oil pressure obtained based on the transfer characteristic is compared with the initial pressure. It is determined a start timing of the engine output increasing control has been reached upon decrease of the estimated pressure to the initial pressure.

Claim:

What is claimed is:

1. A controller for an automatic transmission wherein oil pressures acting on a plurality of frictional engaging elements are individually controlled by oil pressure controlmeans to selectively switch the frictional engaging elements between engagement and release, resulting in a switching from one shift range to another in a shift mechanism, the controller comprising: engine output increasing control means for performingan engine output increasing control to increase an engine output without depending on a driver's accelerator operation when the shift mechanism is down-shifted on the basis of the driver's intention of deceleration, the engine output increasing controlmeans setting an output increase control quantity in such a manner that an engine torque corresponding to a desired engine speed change rate is produced during the engine output increasing control.

2. A controller for an automatic transmission according to claim 1, wherein the engine output increasing control means sets the output increase control quantity on the basis of both a change in gear ratio caused by the down-shift of the shiftmechanism and a shift time during the engine output increasing control.

3. A controller for an automatic transmission according to claim 1, wherein on the basis of deceleration of a vehicle body during the engine output increasing control the engine output increasing control means corrects the output increasecontrol quantity so as to decrease the output during deceleration and increase the output during acceleration.

4. A controller for an automatic transmission according to claim 1, further comprising road surface gradient determining means for determining a gradient of a vehicle running road surface, and wherein on the basis of a road surface gradientdetermined by the road surface gradient determining means in the engine output increasing control the engine output increasing control means corrects the output increase control quantity so as to decrease the output in the case of an up gradient andincrease the output in the case of a down gradient.

5. A controller for an automatic transmission according to claim 1, wherein the engine output increasing control means sets the output increase control quantity in consideration of a response delay after issuance of a command value for theoutput increase control quantity until actual increase or decrease of the engine output.

6. A controller for an automatic transmission according to claim 1, wherein the engine output increasing control means sets a target engine speed so as to afford the desired engine speed change rate during the engine output increasing control,and feedback-controls the output increase control quantity.

7. A controller for an automatic transmission according to claim 1, further comprising intake air quantity detecting means for detecting an amount of intake air introduced into the engine, and wherein the engine output increasing control meansincreases the intake air quantity during the engine output increasing control and corrects an increase quantity of the intake air quantity on the basis of the intake air quantity detected by the intake air quantity detecting means.

8. A controller for an automatic transmission according to claim 1, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine output increasingcontrol, the engine output increasing control means promotes a decrease of a working oil pressure in a frictional engaging element controlled for release.

9. A controller for an automatic transmission according to claim 1, wherein the engine output increasing control means performs the engine output increasing control when shifting is made forcibly to an engine brake-acting shift range by adown-shift which occurs with operation of brakes by the driver.

10. A controller for an automatic transmission according to claim 1, wherein the engine output increasing control means performs the engine output increasing control in the case of a down-shift based on the driver's intention of decelerationand when a vehicle body deceleration is not smaller than a predetermined value.

11. A controller for an automatic transmission according to claim 1, further comprising road shape determining means for determining a road shape of a vehicle running road, and road shape down-sift execution means for executing a down-shift onthe basis of the result of the determination made by the road shape determining means, wherein the engine output increasing control means performs the engine output increasing control when the down-shift is executed by the road shape down-shift executionmeans.

12. A controller for an automatic transmission according to claim 1, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine output increasingcontrol, the engine output increasing control means promotes a decrease of a working oil pressure in a frictional engaging element controlled for release and promotes an increase of a working oil pressure in a frictional engaging element controlled forengagement.

13. A controller for an automatic transmission according to claim 1, wherein the engine torque that is produced results in an increase in engine torque by an amount that corresponds to an inertia torque of at least one member whose rotation isrequired to increase in the down-shift in the shift mechanism.

14. A controller for an automatic transmission according to claim 1, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine output increasingcontrol, the engine output increasing control means promotes an increase of a working oil pressure in a frictional engaging element control led for engagement.

15. A controller for an automatic transmission according to claim 1, wherein, in the case of a manual down-shift representing a down-shift which occurs upon operation of a shift lever or a switch by the driver, or in the case of an autodown-shift representing a down-shift which occurs upon deceleration of a vehicle body or operation of brakes, or in the case of a coast down-shift representing a down-shift which occurs in accordance with a shift schedule preset by a shift line, theengine output increasing control means executes the engine output increasing control and changes an engine output increase quantity or a target value thereof among the manual down-shift, the auto down-shift and the coast down-shift.

16. A controller for an automatic transmission according to claim 15, wherein the engine output increasing control means makes control so that the manual down-shift or the auto down-shift becomes larger in the engine output increase quantity orthe target value thereof than the coast down-shift.

17. A method of controlling an automatic transmission wherein oil pressures acting on a plurality of frictional engaging elements are individually controlled by oil pressure controller to selectively switch the frictional engaging elementsbetween engagement and release, resulting in a switching from one shift range to another in a shift mechanism, the method comprising: performing an engine output increasing control to increase an engine output without depending on a driver's acceleratoroperation when the shift mechanism is down-shifted on the basis of the driver's intention of deceleration, setting an output increase control quantity in such a manner that an engine torque corresponding to a desired engine speed change rate is producedduring the engine output increasing control.

18. A method of controlling an automatic transmission according to claim 17, wherein the output increase control quantity is set on the basis of both a change in gear ratio caused by the down-shift of the shift mechanism and a shift time duringthe engine output increasing control.

19. A method of controlling an automatic transmission according to claim 17, wherein the output increase control quantity is corrected on the basis of deceleration of a vehicle body during the engine output increasing control so as to decreasethe output during deceleration and increase the output during acceleration.

20. A method of controlling an automatic transmission according to claim 17, further comprising determining a gradient of a vehicle running road surface, and wherein on the basis of a road surface gradient determined in the engine outputincreasing control, the output increase control quantity is corrected so as to decrease the output in the case of an up gradient and increase the output in the case of a down gradient.

21. A method of controlling an automatic transmission according to claim 17, wherein the output increase control quantity is set in consideration of a response delay after issuance of a command value for the output increase control quantityuntil actual increase or decrease of the engine output.

22. A method of controlling an automatic transmission according to claim 17, wherein a target engine speed is set so as to afford the desired engine speed change rate during the engine output increasing control, and the output increase controlquantity is feedback-controlled.

23. A method of controlling an automatic transmission according to claim 17, further comprising detecting an amount of intake air introduced into the engine, and wherein the intake air quantity is increased during the engine output increasingcontrol and an increase quantity of the intake air quantity is corrected on the basis of the detected intake air quantity.

24. A method of controlling an automatic transmission according to claim 17, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine outputincreasing control, the engine output increasing control means a decrease of a working oil pressure in a frictional engaging element controlled for release is promoted.

25. A method of controlling an automatic transmission according to claim 17, wherein the engine output increasing control is performed when shifting is made forcibly to an engine brake-acting shift range by a down-shift which occurs withoperation of brakes by the driver.

26. A method of controlling an automatic transmission according to claim 17, wherein the engine output increasing control is performed in the case of a down-shift based on the driver's intention of deceleration and when a vehicle bodydeceleration is not smaller than a predetermined value.

27. A method of controlling an automatic transmission according to claim 17, further comprising determining a road shape of a vehicle running road, and executing a down-shift on the basis of the result of the determined road shape, wherein theengine output increasing control is performed when the down-shift is executed by the road shape down-shift execution means.

28. A method of controlling an automatic transmission according to claim 17, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine outputincreasing control, a decrease of a working oil pressure in a frictional engaging element controlled for release is promoted and an increase of a working oil pressure in a frictional engaging element controlled for engagement is promoted.

29. A method of controlling an automatic transmission according to claim 17, wherein the engine torque that is produced results in an increase in engine torque by an amount that corresponds to an inertia torque of at least one member whoserotation is required to increase in the down-shift in the shift mechanism.

30. A method of controlling an automatic transmission according to claim 17, wherein, in a down-shift involving execution of the engine output increasing control, as compared with a down-shift not involving execution of the engine outputincreasing control, an increase of a working oil pressure in a frictional engaging element controlled for engagement is promoted.

31. A method of controlling an automatic transmission according to claim 17, wherein, in the case of a manual down-shift representing a down-shift which occurs upon operation of a shift lever or a switch by the driver, or in the case of an autodown-shift representing a down-shift which occurs upon deceleration of a vehicle body or operation of brakes, or in the case of a coast down-shift representing a down-shift which occurs in accordance with a shift schedule preset by a shift line, theengine output increasing control is executed and an engine output increase quantity or a target value thereof among the manual down-shift, the auto down-shift and the coast down-shift is changed.

32. A method of controlling an automatic transmission according to claim 31, wherein control is made so that the manual down-shift or the auto down-shift becomes larger in the engine output increase quantity or the target value thereof than thecoast down-shift.